Sassanian Persia was known in China as par-sig, which represents Midddle Persian pārsīg. The pronunciation of these Chinese characters was fa-si in Old Japanese and the modern pronunciation is ha-shi. Chinese people of the fourth century correctly transliterated into Chinese characters while modern Japanese people have applied hashi vaguely from the Greek-Latin name of Persia. Incidentally, Parthia was known as an-siək in the Han dynasty. an represented Iranian ar, so An-siək responded with Aršak, the founder of Parthia. The king of Aršak founded the country (or city) of p‘an-təu, which represented Parthian partav ‘Parthian’.
Eiich Imoto, “Mihrak and other Iranian words’, Orient, XVIII, 1982, 129.